The present invention relates to an accurate method and apparatus for controlling the flow rate of intake air of an engine.
There are two general types of methods for controlling fuel injection type engines. One is the air-first control system in which air taken into the cylinders of an engine (hereinafter referred to as "engine intake air flow rate. The result of measurement by an air flow meter provided in a intake pipe is simply referred to as "air flow rate", is measured and then the fuel is injected in an amount in accordance with the engine intake air flow rate. The other is the fuel-first control system in which an amount of fuel is defined in advance and an engine intake air flow rate in accordance with the same is supplied to the engine.
In either of the systems, it is important to achieve an air fuel ratio that realizes a state of combustion desirable for reduction of harmful components in exhaust gas and reduction of the amount of fuel consumption.
Referring to the air-first control system, methods for controlling an internal combustion engine aimed at maintaining an air fuel ratio accurately during a transient time are disclosed in, for example, Japanese patent Application Laid-Open 104930/1990 (hereinafter "first prior art") and Japanese patent Application Laid-Open 134136/1992 (hereinafter "second prior art").
In the first prior art, a technique is disclosed in which an amount of fuel injection is determined by calculating a flow rate of intake air to an engine in accordance with a model of a intake pipe. In this case, a delay in an engine intake air flow rate at the time of a movement of a throttle valve caused by an accelerator pedal is calculated using pressure and engine speed information, and the amount of fuel injection is corrected in association with the delay of air. Since this method has had a problem in that amount for fuel correction is slow because the correction is calculated after a change in the opening of the throttle valve occurs, the second prior art provides a fuel injection controller by introducing a delay to the opening of the throttle valve relative to an acceleration pedal stepping-on amount to reduce the effect of the correction delay.